Featured Research

Monopoly of the male orangutan: Comparative field observations on Sumatra and Borneo

Date:

March 5, 2013

Source:

Swiss National Science Foundation

Summary:

The sexual development, mating habits and social hierarchy of the orangutans are more heavily dependent on their environment than had previously been assumed: where the rain forest supplies more food, the influence of the dominant male increases. In order to escape his attention, many other males remain "small."

The sexual development, mating habits and social hierarchy of the orangutans are more heavily dependent on their environment than had previously been assumed: where the rain forest supplies more food, the influence of the dominant male increases. In order to escape his attention, many other males remain "small."

Related Articles

This is the conclusion of a study supported by the Swiss National Science Foundation (SNSF).

In Malay, the word "orangutan" means man of the woods. In fact, however, these rain forest dwellers clad in a reddish-brown coat are our most distant relatives within the great ape family. The orangutan differs from all of the others because the male can go through two different phases of development. It is for this reason that there are two types of sexually mature males, the smaller appearing externally like the female and the larger developing secondary sexual characteristics such as cheek pads and throat pouches.

Arrested development

Certain small males may remain at an arrested stage of development for years or even throughout their lives without the final spurt of growth ever arriving. As Lynda Dunkel, holder of a Marie Heim-Vφgtlin scholarship of the SNSF, and her colleagues at the Anthropological Institute and Museum of Zurich University have now shown, this developmental arrest occurs more frequently on Sumatra than on Borneo, the other south-east Asian island which is home to the orangutans.

On Sumatra, the researchers observed twice as many small males as adults with cheek pads. During a five-year period of observation in the rain forest, only a single male was seen to develop secondary sexual characteristics. By way of contrast, on the island of Borneo, there are twice as many males with cheek pads as without.

Forced copulation

These males engage in disputes for the favour of fertile females much more often than those on Sumatra where, within the area under observation, a single dominant male monopolises sexual relations with the females. As there is more food available in the jungle on Sumatra than in the forests of Borneo, the dominant male has sufficient time to keep a close watch over the females in his environment and he drives out any other males with cheek pads before they can mate with a female.

However, smaller males without secondary sexual characteristics are less conspicuous. On Sumatra, this makes it easier for them to copulate with a female, even though the females put up resistance in 60% of the cases observed. Forced copulation also takes place on Borneo. There, however, as the males are constantly engaged in fighting in which the smaller ones never prevail, the advantages of developmental arrest disappear.

The fact that food supply in the forest has such a strong impact on the mating behaviour of the orangutan came as a surprise to Dunkel. "It goes to show," she says, "that the organisation of these great apes -- and perhaps that of our ancestors as well -- is more variable than we had hitherto assumed. Apparently, natural selection not only moulds appearance but also adapts social behaviour to the conditions of the local environment."

Swiss National Science Foundation. "Monopoly of the male orangutan: Comparative field observations on Sumatra and Borneo." ScienceDaily. ScienceDaily, 5 March 2013. <www.sciencedaily.com/releases/2013/03/130305080648.htm>.

Swiss National Science Foundation. (2013, March 5). Monopoly of the male orangutan: Comparative field observations on Sumatra and Borneo. ScienceDaily. Retrieved March 31, 2015 from www.sciencedaily.com/releases/2013/03/130305080648.htm

Swiss National Science Foundation. "Monopoly of the male orangutan: Comparative field observations on Sumatra and Borneo." ScienceDaily. www.sciencedaily.com/releases/2013/03/130305080648.htm (accessed March 31, 2015).

More From ScienceDaily

More Plants & Animals News

Featured Research

Mar. 31, 2015  Researchers have recorded the first direct observations of the micro-scale mechanisms behind the ability of skin to resist tearing. The results could be applied to the improvement of artificial skin, ... full story

Mar. 31, 2015  Soil organic matter, long thought to be a semi-permanent storehouse for ancient carbon, may be much more vulnerable to climate change than previously thought. Scientists have found that the common ... full story

Mar. 31, 2015  Using the assessment tool ForWarn, US Forest Service researchers can monitor the growth and development of vegetation that signals winter's end and the awakening of a new growing season. Now these ... full story

Mar. 31, 2015  Until now electric fences and trenches have proved to be the most effective way of protecting farms and villages from night time raids by hungry elephants. But researchers think they may have come up ... full story

Mar. 31, 2015  The endangered desert pupfish has made itself at home in the harsh, hot environment of Death Valley hot springs by using a surprising evolutionary adaptation: They can go for up to five hours without ... full story

Mar. 31, 2015  Researchers have detected a human fingerprint deep in the Borneo rainforest in Southeast Asia. Cold winds blowing from the north carry industrial pollutants from East Asia to the equator, with ... full story

Mar. 31, 2015  A team of engineers and biologists reports new progress in using computer modeling and 3D shape analysis to understand how the unique grasping tails of seahorses evolved. These prehensile tails ... full story

Mar. 31, 2015  As the five-year anniversary of the explosion of the Deepwater Horizon oil rig approaches, a new report looks at how twenty species of wildlife are faring in the aftermath of the ... full story

Mar. 31, 2015  Scientists have uncovered the earliest fossilized evidence of an insect caring for its young. The findings push back the earliest direct evidence of insect brood care by more than 50 million years, ... full story

Giant Amphibian Fossils Found in Portugal

Reuters - Light News Video Online (Mar. 31, 2015)  Scientists discover a new species of giant amphibian that was one of the largest predators on earth about 220 million year ago. Tara Cleary reports.
Video provided by Reuters

Bionic Ants Could Be Tomorrow's Factory Workers

Reuters - Innovations Video Online (Mar. 30, 2015)  Industrious 3D printed bionic ants working together could toil in the factories of the future, says German technology company Festo. The robotic insects cooperate and coordinate their actions and movements to achieve a common aim. Amy Pollock reports.
Video provided by Reuters

Related Stories

Feb. 2, 2015  'Foot' travel by Borneo's shaggy apes may be evolving more than initially thought, researchers have discovered. The Bornean orangutan not only regularly walks Wehea Forest floors to ... full story

Feb. 13, 2014  Orangutans come down from the trees and spend more time on the ground than previously realized -- but this behavior may be partly influenced by humans, a new study has found. The research is based on ... full story

July 29, 2013  Orangutans might be the king of the swingers, but primatologists in Borneo have found that the great apes spend a surprising amount of time walking on the ground. The research found that it is common ... full story

Oct. 16, 2012  The orangutans in Sumatra are in danger of becoming extinct. Anthropologists now prove that only recently this ape species saw a drastic decrease in population. For the first time, they studied the ... full story

ScienceDaily features breaking news and videos about the latest discoveries in health, technology, the environment, and more -- from major news services and leading universities, scientific journals, and research organizations.